How do you solder components with a lot of thermal mass and a big pad beneath it

[technix]

A.K.A. surface mount aluminum caps. I am getting very frustrated at this to the point that I am on the verge of writing off my boards, although it seem to me as they should be otherwise perfectly okay.

[mikeselectricstuff]

Metcal or JBC iron.

[tszaboo]

They are p.i.t.a to manually solder. Basically the leads are under the package like a QFN, but you are working with big thermal mass, unlike QFN. I usually give some extra pad next to it, which I can heat up with the iron.

[AndyC_772]

Metcal or JBC iron.

... with a tip that's big enough to get enough heat conducted into the board. Use a larger tip size that you might ordinarily choose for the size of component pad you're working with.

I decided to buy a JBC after I saw a demo of one being used to solder wires to coins.

[Bud]

Preheating the board helps. I just use my hot air station to warm up the area from below, then use the soldering iron. Still doing this even if my soldering iron is JBC.

[max_torque]

Two tricks:

Buy a cheap hot plate, but make sure it's got a "low" setting, ie around 100degC

Stick you pcb, and caps on that, let it take the chill off the parts.  (experiment first with some scap pcbs and old caps to find out what temp setting works best!  It wants to be below the melting point of the solder by some margin, the aim is to just 'take the chill off' the parts)

Then use a hot air gun to warm the cap and top side pcb copper.  If you're using solder paste, then just the hot air gun will then work, but if you're using normal solder and an iron, you'll need to get the tip of the iron onto the pad next to the cap. here, as others have mentioned, a bigger pad really helps, especially with Cap packages that put the tabs under the cap!

And with all things soldering, get a syringe of BGA rework flux.  This is viscous flux, which stays where it's put and a small blob dab'd onto the pads before you place the cap wil make a massive difference to the heat flux from your iron into that pad!

[james_s]

I use a temperature controlled iron with a wedge tip, I find it to be a good all around tip that I use for almost everything. A lot of people seem to think you need a tiny needle tip to solder SMD parts but the problem with those is they can't carry enough heat to the pad. A hotplate also works well, I built a custom one for reflow soldering but I've seen people do it in a pan on the stove even.

[dl1640]

We use a Hakko high power station at work, to deal with big thermal mass.

[Someone]

Lots of good advice here so far, also if you know there will be hand assembly or rework then extend the pads out beyond the footprint of the part so you have a place to put the soldering iron tip. Not much help on a pre-existing board but those are the little details which can make life easier.

[t1d]

A regular clothes iron. Remove water. Hold it upside down. Look on YT for instructions for this... Look under DIY SMD techniques. Also, see Mr. Carlson's Lab, for instructions on making a tip for the high heat, gun-style, soldering guns. Borrow one from a friend and make the tip out of copper wire. Also, look for a MakerSpace club in your area, for extra expertise and tools.